Abstract
Purpose High-translucent dental zirconia has been introduced as a suitable material for anterior monolithic restorations. The material composition differs from traditional 3Y-TZP both with regard to yttria content and grain size. Little is known regarding how these alterations affect other properties than translucency and flexural strength. The aim of this study was to evaluate the crack propagation resistance and hardness of dental zirconias with different yttria content and different manufacturing methods. Materials and methods Measurement of hardness (HV2/5) and crack propagation from the indents (damage tolerance) was performed using a hardness tester(Vicker) on a flat polished surface of five crowns from six different commercial dental zirconias; one hard-machined 3Y-TZP, three soft-machined 3-5% yttria-stabilized zirconias and two soft-machined zirconias with ≥5% yttria content. Results Damage control varied greatly among dental zirconias with different compositions and fabrication methods. The hard-machined 3Y-TZP had better crack propagation resistance than soft-machined, 3-5% yttria-stabilized zirconias Conslusion The ultra-translucent zirconias with ≥5% yttria content had the lowest crack propagation resistance. Hardness is not a suitable indicator for damage tolerance.
Highlights
There has been a rapid devolvement in dental zirconia materials towards more translucent and tooth-colored materials [1,2]
High-translucent dental zirconia has been introduced as a suitable material for anterior monolithic restorations
The material composition differs from traditional 3Y-TZP both with regard to yttria content and grain size
Summary
There has been a rapid devolvement in dental zirconia materials towards more translucent and tooth-colored materials [1,2]. The sintering temperatures or hold times affect the grain size as well as the crystal lattices [1,9,10]. This will reduce the number of borders where the light transmission can be affected in the passage through the material and reduce scattering which makes the material appear white and opaque. Personal experience and communication with dentists and dental technicians indicate that margin chipping is more frequent with the ultra-translucent materials (Figure 1). Margin damages can be detrimental for crown strength [13,14,15,16]
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